If you grow cactus and succulents as houseplants, here's the best thing you can do to get these warm-growing, sun-loving plants through the cold, dark days of winter: Lose your watering can.
That's the advice of Nick Daniel, horticulture specialist for the Cactus and Succulent Collection at the Denver Botanic Gardens. Overwatering is the No. 1 reason home growers kill succulents during the winter, said Daniel, who manages the garden's hardy and non-hardy cacti and succulents.
"It's not bugs, it's not under watering," Daniel said about why so many people kill cacti and succulents such as echeverias, aloes and euphorbias when the weather turns cold. "I'd say 75 to 80 percent of the time, people keep watering on a regular schedule, and they are not letting things dry out. They are not appreciating that these succulents oftentimes hit a dormancy as the days grow short, and [continuing to water on a regular schedule] just rots their roots very fast."
That's just one of Daniel's tips for winter care for home-grown cacti and succulents. Here's a 10-point checklist to help keep these fascinating plants healthy and happy until spring.
1. Know the difference between cacti and succulents
Perhaps the first thing Daniel said home growers should understand is that every cactus is a succulent, but not every succulent is a cactus. If that sounds like a tongue twister, here's the explanation and why this is important.
Cacti are a very specific family and are native to North, Central and South America. Many plant families, on the other hand, include succulents among their members — the sunflower family and the cucumber family, for example — that don't classify as cacti.
"A lot of people will try and apply the term cactus to an agave or an aloe or a euphorbia from Africa," explained Daniel. "So, I really try and spend time hammering home in my talks that they all have their own place, and they all have similar environmental adaptations, but succulents are not all in the same family and they are not all cacti."
2. Establish a seasonal calendar
It may sound silly, but to know when to begin a winter-care regimen for cacti and succulents you have to know when winter begins. For indoor growing purposes, that's not at the winter solstice, which occurs around Dec. 21.
As a rule of thumb, Daniel said to switch to winter-growing mode when the days start shortening as fall kicks into high gear. This is when you should start moving plants you've put outdoors for the summer back inside, definitely transferring all plants before the first frost. When December rolls around and daylight has become really short, it's time to go into a strict winter care schedule.
The same rule applies for the summer solstice. You don't have to wait until June 20 to 22 to move plants back outdoors. It's safe to do this as days start to lengthen again, usually in mid-March or early April, when Daniel says your cacti and succulents are going to start getting really hungry and thirsty. However, be sure to wait to do this until all danger of frost has passed.
3. Give your plants a winter home in the brightest light possible
Unless you live in an especially dark home, there's no need to invest in a grow light arrangement to get cacti and succulents through winter. Low light levels aren't nearly as big a deal for winter care as over watering, said Daniel.
Simply placing your plants where they will receive the brightest light possible should be sufficient to keep plants compact and colorful during the few cold months of the year. Daniel realizes your brightest spot might not be the most aesthetically pleasing place to enjoy all your plants. But he says to remember that you can rotate plants, moving them from window to window so that you'll always have some of your favorites in view.
Growers in northern climates, as well as those in mild climates that sometimes experience cold snaps, should not place cacti and succulents too close to windows. "Bitter cold coming in through the glass can make them really unhappy really fast," advised Daniel.
4. Group your plants according to their specific needs
If you have a large number of plants or a collection that varies in the number of species, you may find that it helps to group them indoors according to their light and water needs. This mimics in a small scale what Daniel says he does in the greenhouse at the Denver Botanic Garden. "I have stuff from all over the world, and I have them mixed together by water and other requirements."
There is so much information about these groups online that Daniel said you should be able to learn what your specific plants need with just a little bit of research.
5. Limit watering and stop feeding
While cacti and succulents have very similar water storage tissues and similar growth rates, Daniel said cacti need to be treated a little differently from most succulents. The most important difference is that cacti tend to be more prone to rot than succulents, so they need a drier winter period than succulents.
"I try to teach people to think in terms of what you are not seeing, what's happening below the soil," said Daniel. "All succulents, the cacti very specifically, rely on their root hairs for nutrient uptake and erosion control. Once those root hairs start rotting from being over watered, it's a pretty fast downward spiral. However, they can handle drying out to a degree."
The goal is to water cacti just enough to keep their roots happy — which is enough to prevent them from completely drying up and shriveling. Think of it this way: Cacti are not going to flower in the winter and they are not going to grow much. So they don't need much water and they should not be given any fertilizer from September through March.
The no-feeding rule also applies across the board with succulents, because giving them extra nitrogen when their growth rate has slowed significantly in winter can stress them out and lead to quick rotting. Succulents such as hens and chicks, echeverias, aloes and others can still be watered, but should be allowed to dry out between watering.
6. Find a sweet spot with watering
Daniel has an easy way to determine when to water cacti and succulents in the winter.
"I like to put my finger in the soil down to the first knuckle," he said. "If the soil is dry, I think it's fine to go ahead and water. If it's moist, hold off watering for another couple of days. Wait until the soil gets a little bit drier so you can be on the safe side. Being drought-tolerant plants, in general, you have a lot more give and take where you are not going to kill cacti and succulents by letting the soil go completely dry. And that helps hedge your bets against overwatering your plants and rotting them, because that's what I think is much more dangerous any time of year, but especially in the winter when low light and over watering and feeding are big issues."
7. Control insect damage
Homes tend to be dry, especially in the winter when the furnace is running or there's a fire going. Insects such as armored scale and mealy bugs enjoy these dry environments as much as people, and they are as happy to take up residence among cacti and succulents as they are on pothos or other houseplants.
If you find these or other insects on your cacti and succulents, don't use a horticultural oil on them like you might use on other plants. These soaps and oils will eat away at the waxy skin layers of cacti and succulents and desiccate them, much like they do on the insects.
"What I highly recommend," said Daniel, "is letting the soil fully dry out, then just dabbing a Q-tip into everyday 70 percent rubbing alcohol and press it against the insects. This will do a very good job for the home grower without using nasty systemic pesticides."
If you discover an insect population that's gotten out of hand, you can put the alcohol in a spray bottle and spray the plants with this. Because there will be runoff from the plants, it's best to do this at a kitchen or bathroom sink — or outdoors if you are lucky enough to get a mild winter day.
8. Move plants outdoors in the spring
When spring returns, consider moving your plants outdoors. Daniel thinks too many people get stuck on leaving them indoors, which he says is unfortunate. Cacti and succulents "just love the direct sun, the moving air and a little extra heat. It gets them to root better and stresses them into flowering a little more."
But when you make that transition, do it gradually. The plants need time to adjust to brighter light, so move them in stages into the brightest light you are going to give them. Daniel advised this should take place over 10 to 14 days. Begin with keeping the plants in almost total shade for the first few days that they are outside.
"If you put them directly into full sun, all these plants will sunburn," said Daniel. The damage from sunburn shows up as black marks for which there is no cure. "I understand why people think well … it's a cactus, you're a succulent, so you can just take the bright light." But that's just not the case after the plants have been in low-light conditions for several months.
9. Where to find more information
Sometimes home growers will panic because they want more information about a cool succulent they've bought but they've thrown away the name tag. The fear comes from not knowing how to research the plant because they don't know what it is. Not to worry, says Daniel, there's a pretty easy way to find out what you've got.
Take a photo of it and send it to your state Extension service, call help lines at botanic gardens or contact one of the many cactus and succulent societies around the world.
"Those are going to be really, really wonderful resources for finding cultural requirements for pretty much any succulent that's available to an average home grower in the United States," said Daniel. You can follow a similar procedure if you find critters on your plants but aren't sure what they are, or see other problems. "I get emails forwarded to me all the time for identification of insect problems, water issues, all that stuff," Daniel added.
He knows reaching out for help works because he's even done it himself! If you want to reach out to Daniel, you can contact him at: firstname.lastname@example.org.
10. Don't overthink how to grow these really neat plants
Daniel finds in his talks and through his work at the Denver garden that there is a lot of interest in cacti and succulents, especially among millennials. But he's also seeing something else.
"One of the biggest things I run into is that people are overthinking how to grow them. Too many people are too quick to over analyze every aspect of their cacti or succulents at home when, really, that's not necessary. They've survived on this planet longer than we have for a reason. People always want to water their plants on a set schedule. But with these plants it's just not like that. Let that soil dry out, provide the brightest light possible, take a deep breath and then sit back and relax and enjoy them."